Perpendicular magnetic recording (PMR) is important for the future of the magnetic recording industry because it offers higher areal density than the current longitudinal magnetic recording (LMR). This is due to the fact that the PMR medium is thermally more stable than that used for LMR. At present, LMR has achieved over 100 Gigabits per square inch (Gbpsi) in the laboratory and more than 60 Gpsi in products currently offered at the market place. In order to further extend the LMR recording density, two main obstacles have to be overcome. The first one is the thermal stability of the LMR recording media which arises because its thickness has to decrease to the extent that thermal energy could randomize the recorded bits. The second one is the ongoing increase in the write field needed to record on the high coercivity LMR media.
This high coercivity is needed to achieve high bit resolution and good thermal stability. Both obstacles to LMR would be considerably lowered if PMR were deployed instead. Thicker PMR media with a magnetically soft under-layer film (SUL) could be used to alleviate the thermal stability problem. A PMR writer provides a larger write field than that of LMR, which is limited to the fringe field from its write gap.
An example of a perpendicular writer of the prior art is shown in FIG. 1. Magnetic yoke 11 is surrounded by write coil 12 and includes main pole 13 that terminates as a write pole tip at the recording surface. Return pole 14 conveys the magnetic flux generated by coil 12 down to a short distance from the recording surface. The flux passes from write pole 13 through recording layer 16, into SUL 17, and then back up into return pole 14
Currently, the single pole is usually made of high Bs (saturation flux density—measured in Teslas) material, with values >2T, and has very small dimensions (0.1 μm in width and 0.2 μm in thickness) together with a relatively long yoke. As a result, the single pole has very large shape anisotropy. After the writing process, the remnant field from a single pole can be very large (as high as 2 kOe), which usually causes erasure of written bits. This problem will get more severe with further decreases in device dimensions.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 5,477,007, Shukh et al describe a top pole having a laminated structure. In U.S. Pat. No. 6,278,590 Gill et al disclose a laminated pole. U.S. Pat. No. 6,396,735 (Michijima et al) shows a laminated memory element. Sasaki teaches that a top pole may be laminated of two or more materials in U.S. Pat. No. 6,255,040. In U.S. Pat. No. 5,621,592, Gill et al disclose a laminated Fe-based/NiMn structure for a write pole while Mallary shows a vertically laminated pole in U.S. Pat. No. 5,108,837. Note that all these references relate to LMR and are not applicable to perpendicular recording systems in the forms and dimensions described.